This invention relates to the electric power supply equipment and method which supply stable a constant voltage power to a load.
As is well known, some electric power supply equipment, includes a circuit for detecting abnormalities in load, and restricts the load current for protection of the circuit. Other circuits detects the power failure and switch the electric power supply to a backup power source.
Formerly, for protecting the circuit against excessive loading, as mentioned above, various heat-sensitive resistance devices such as thermisters, posistors, current limiters and thermal shut-downs were used. Because of lack of quick responsiveness, these heat-sensitive resistance devices cannot limit the output current readily in abnormal incidents, such as load short-circuit, and may, therefore, damage circuit devices in power failure detector circuits, regulators and other circuits, thus causing insulation deterioration, the breaking of primary windings, the destruction of rectifier circuits and so on.
Furthermore, because of wide dispersion in their characteristics, heat-sensitive resistance devices create problems in setting arbitrarily and accurately the detection threshold values for detecting load abnormalities.
Further, with conventional power supply equipment the cost becomes high due to the need for many parts, since the failure detection circuit is provided separately from other circuits, such as a regulator.